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My DAW computer is plugged in to a Furman power conditioner but I still get a a lot of noise through the electrical lines in our house. When it is acting up it will record on whatever track I'm working on!
I've checked with out electric co-op. They confirmed that the noise is a problem with their supply, but they don't have any ideas other than adding in another suppressor before the computer.
Does anybody have a recommendation for a good suppressor?

Balanced power is a good, but expensive option. You could try building a Faraday cage, also expensive. You could try a fancier grounding scheme, but depending on your location, it might be a code violation. Using balanced cabling wherever possible helps, as does careful gain staging. Unbalanced analog cables can act as an antenna; keep the length of those to a bare minimum. There are some tweaks that can be made to amplifiers in your setup that can be made by a qualified technician, including adding hematite beads at strategic locations in the audio path and power supplies. Could be you just need a more robust RFI filter, but if you're getting clunks from a fridge compressor kicking on, what you need is a voltage regulator, available from Furman and others, expect to pay at least $350, and it'll likely feature beefier RFI protection, in the bargain. Having your studio's power outlets on their own isolated circuit could provide some relief, but since you've established that the power coming in is dirty, I doubt that option is worth pursuing.

What sort of noise is it ? A mains hum ?

You can filter those out quit well , there's a preset on one of the Waves plugins..either X-Noise or Z-Noise for 50hz & 60hz hum that notches out the fundamental and various harmonics

Have you tried something like this to get rid of it from the recording ?

https://www.thomann.de/gb/ebtech_by_mor ... hopzillagb

Mark

What other equipment are you using? Guitar amps, keyboards, interfaces etc. should all be using the power conditioner. Check if any of your units have earth-defeat switches on them and try activating those.
If you play electric guitar then pointing it a different direction when playing can make a difference, especially with single-coil pickups. If a guitar amp is close to the DAW computer then try rotating it 90 degrees to the computer (trial and error).

However, as already stated by @mojobone, if the source is dirty then there is little you can do. You can only hope that all these small changes will add-up to something workable.

Good luck